The invention generally relates to a vortex reducing mower blade and, more particularly, to a mower blade arranged in accordance inventive structures for managing and/or reducing the production and/or strength of vortices in the wake of the trailing corners of the blade tips.
It is an object of the invention to provide a rotary mower blade with vortex reducing structures to reduce the production and/or strength of vortices in the wake of the trailing corners of the blade.
It is an alternate object of the invention that the above vortex reducing mower blade reduce the production and/or strength of vortices in the wake of the trailing corners of the blade such that the vortices do not interfere with or decrease the suction (or lift) effect created by the airlifts in the trailing edges of the blade.
It is an additional object of the invention that the foregoing vortex reducing mower blade provide a more even trim of grass rather than an uneven trim seen when vortex production and or strength is too great.
It is a further object of the invention that the foregoing vortex reducing mower blade allow slower speed of operation to get the same suction power as given by a conventional blade not having vortex reducing structures operated at a higher speed.
These and other aspects and objects are provided according to the invention in a vortex reducing mower blade for use with a rotary lawn mower having a motor and a depending drive shaft has a cutting edge on each leading edge thereof, an airlift on each trailing edge thereof, and outboard ends extending between the terminations of the leading and trailing edges. The outboard ends generally meet with the trailing edges at respective trailing corner- or tip-regions. Each outboard end has margins formed as a boundary-layer fence that is angled either upwardly or downwardly relative to a given relative up direction which is parallel to the central axis of the depending drive shaft. These boundary-layer fences reduce the production and/or strength of vortices in the wake of the trailing corner- or tip-regions of the blade. Each boundary-layer fence may be angled either upwardly or downwardly at generally a right angle. To produce a blade this way, generally the blade might be produced from flat steel stock including that each boundary-layer fence is formed as separate weldment from comparable flat steel stock for attaching in position by means of welding. Alternatively, each boundary-layer fence may be angled either upwardly or downwardly in generally a curving sweep. Producing a blade this way can be accomplished by producing the blade as a unit from a single stock piece of flat steel including that the boundary-layer fences are configured therein by means of a brake, stamping or press-forming operation.
Another way of reckoning the vortex reducing mower blade includes the following. It comprises an elongated mower blade extending span-wise between spaced outboard ends. A central mounting portion allows mounting to a depending spindle. There are leading cutting portions proximate the outboard ends of the blade which are formed with respective leading cutting edges for rotating through a common cutting plane. There are also trailing lift portions respectively located behind the leading cutting portions and inclined upwardly from the cutting plane to terminate in trailing edges.
Wherein the location where each pair of trailing edges and outboard ends meet generally happens to define a respective trailing corner- or tip-region. Proximate each outboard end the blade further includes a chord-wise extending boundary-layer fence. Each boundary-layer fence is angled either upwardly or downwardly and as previously mentioned, acts to reduce the production and/or strength of vortices in the wake of the trailing corner- or tip-regions of the blade.
Generally speaking, absent the vortex reducing structures, the mower blade is conventional in at least some of the following respects. It is a rotary mower blade adapted for rotation about an upright axis. It extends span-wise between spaced end portions that terminate in outboard edges. Each end portion extends chord-wise between a leading flat portion sharpened to define a cutting edge and a trailing lift portion joined to and angled upwardly in trailing relationship to the leading flat portion and terminating in a trailing edge. The inventive improvement of said vortex reducing mower blade relates to a boundary-layer fence proximate to or forming a margin of the outboard edge of each lift portion. Each boundary-layer fence is angled either upwardly or downwardly as for reducing the production and/or strength of vortices in the wake of the trailing corner- or tip-regions of the blade.
It is an inventive aspect that each boundary-layer fence may be angled downwardly and given the shape of such a wedge as defined between an upper border common with the respective upwardly-angled lift portion and a lower border defined by an imaginary trailing continuation of the outboard edge of the respective leading flat portion. Each boundary-layer fence may be angled upwardly or downwardly in either a sharp right angle or else a curving sweep. If angled in a curving sweep, then each boundary-layer fence may be angled in the curving sweep such that the termination of which is generally oriented straight up or down as applicable.
Preferably but without excluding any other configuration, the trailing edges extend generally straight and generally parallel to a span-wise-extending plane containing the upright axis. Likewise, preferably but without excluding any other configuration, the outboard edges are generally contained in a chord-wise-extending plane that is parallel to the upright axis such that the trailing corner- or tip-regions are generally right-angled corners.
Optionally the vortex reducing mower blade may further comprise one or more span-wise spaced, chord-wise elongated vortilons distributed across either the upper or lower surfaces of the end portions.
Additional aspects and objects of the invention will be apparent in connection with the discussion further below of preferred embodiments and examples.